Selective transmission system



E. A. LAPORT SELECTIVE TRANSMISS ION SYSTEM Aug. 1o, 1937.

Filed Nov. 19, 1935 O O OYOYO'O'O O O INI/ENTOR.

Edmund A. Lapmi 7U www j ATTURNEY.

Patented Aug. 10, 1937 ETE STA PATENT GFFQE to Wired Radio, Inc.,

New York, N. Y., a corporation of Delaware Application November 19, 1935, Serial No. 50,491

5 Claims.

My invention pertains in general to transmitting systems for conveying intelligence by modulated high frequency energy.

The principal object of my invention consists 5 in providing a transmitter system adapted to selectively transmit modulated high frequency energy in several different senses with respect to the condition of the carrier frequency.

Another object of the invention comprises pro- '10 viding a selectively operable transmitter for supplying a load circuit with various types of modulated high frequency energy.

A still further object of the invention resides in the provision of an electron tube Acircuit sys- ]5 tern controlled by a selective switching arrangement for effecting various circuit combinations tc produce modulated high frequency energy in different forms, including variable carrier as well as suppressed carrier transmission.

These and other desirable objects will be apparent from the following, reference being had to the accompanying drawing which diagrammatically represents one embodiment of the invention.

The invention contemplates providing an arrangement for transmitting modulated high frequency current under different selected conditions of carrier frequency operation. In accordance with the invention, a plurality of circuit combinations are employed whereby the transmission system may be made to generate a carrier frequency of constant amplitude, a carrier frequency of variable amplitude, or suppressed carrier. The system provides a transmitter having a high frequency energy source and a source of modulation energy with a modulator and amplifier arrangement combined with a selective circuit switching organization whereby transmitting energy in the form of fixed carrier and modulation side bands is delivered to the load, variable carrier and modulation side bands are delivered to the load, or fixed modulation side bands with carrier suppressed are delivered to the load.

Referring to the drawing in detail there is v provided a source of high frequency energy I.

This source is any means suitable for providing constant amplitude sustained oscillations of frequencies suitable for carrier purposes in the transmission of intelligence through space or over wire 50 lines. The output of the source I is connected to the control electrode of an amplifier tube 2 included in a high frequency amplifier stage, The tube l as shown here is representative of any suitable means for controlled pre-amplification of the high frequency energy fed to tubes 4 and '5.

The output of the tube 2 is directed through a transformer 3 to the control electrodes of amplier tubes l and 5, these control electrodes being connected with the secondary windings of the transformer 3 in balanced push-pull arrangement. The polarizing voltage for these control electrodes is supplied to the midpoint of the secondary windings of transformer 3 from a suitable source of energy. In accordance with the system as represented, an auxiliary winding 6 is associated with the transformer 3 for supplying energy to an indicating instrument 'I which may be selectively connected therewith through switch 8 for indicating proper conditions of high frequency excitation energy or relative degree of modulation.

The tubes d and 5 may be Type 59 pentode amplifier tubes. The screen electrodes 9 and I0 thereof are connected in parallel and with one of the contacts I6 of a multi-contact double-throw switch II. The suppressor electrode I3 is connected with terminal 3l engageable by the contact I5 of switch II, while the suppressor electrode I4 is connected with the contact I5. The anodes 22 and 23 are connected with the switch contacts Il and I8, respectively, of the switch II.

Terminal 29 of switch I I is connected with terminal 34 and also with one side of a primary winding 3S of an output transformer 49. The terminal 30 is connected with the terminal 33 and with one side of another primary winding 39 of the transformer 4U. The other side of winding 38 is connected to switch contact 2D, while the other side of primary winding 39 is connected with switch contact I9. This circuit arrangement including the switch II in connection with the windings 38 and 39 is for the purpose of selectively connecting the windings 38 and 39 in either parallel or push-pull for various operating conditions of the amplifying tubes i and 5, as will be brought out later in more detail. The output winding 4I of transformer 40 is connected with 132 which is representative of means for the utilization of the transmitted energy and may be a wired radio network or a radiation system or the like. A meter i4 is provided in circuit with the winding 38 for making observations of the anode current of the tubes 4 and 5.

In accordance with the invention, an audio frequency source 46 is provided for supplying modulation energy. The source 46 is representative of any arrangement for providing the desired program or other type of signals. The output of the source 46 is directed through the input transformer 4l and thence through an amplifier tube I8 to an output transformer 49. Under some circumstances this amplifier arrangement may comprise a plurality of stages of amplication and is merely intended to be representative of suitable amplification means. The output transformer 49 includes balanced secondary windings 50 and 5I. One side of the winding 59 is connected with terminal 25 of switch I I, while one side of winding 5I is connected with terminal 3I. The midpoint connection of windings 50 and 5I includes a connection to a suitable source of biasing voltage supplied to terminal 55. The switch 8 is selectively connectible with the `anode circuit of the amplifier tube 48 for permitting observations of the relative modulating voltages @appearing in the system.

The modulation energy source 45 is provided further with output connections toa variable carrier control unit 53 which may be any device capable of delivering a sufficient direct current output voltage which is directly proportional to the audio frequency input voltage. In the present instance, this unit comprises an amplifierrectifier system. 'Ihe output circuit of the unit 53'inc'ludes a connection to terminal 54. The terminal54 is associated with a switch 55 which may contact with either terminal 514 or terminal 55. The terminal 56 includes a connection with the terminal 51 which is in circuit with a suitable source of constant anodefvoltage or B supply. Other circuit components shown but not described are those known in the art for performing lknown electrical functions and are complementary to the' apparatus already described.

In the operation of the system, the high frequency source I supplies amplified constant amplitude high frequency oscillations to the. control electrodes 9 and IIJ of amplifier tubes 4 and V5. The source 46 supplies the modulation energy which is utilizedto control the tubes 4 and5 in various operating'arrangements depending upon the switching positions of switch II and switch 55. First, it will be assumed that it is desired to transfer to the load 42 modulated high frequency energy having constant carrier and normal modulation side bands. Toeifect this condition, the switch :II is movedto a right hand position with the switch contacts I5-20 in engagement with contact terminals 3I-35. The switch 55 is ,then moved to a right hand position'in engagement with contact terminal 56. Forthis condition of the switches yII and 55, the screen electrodes `9 and II] are directly connected through terminals 32 and 56 with the source of constant positive anode voltage supplied to lterminal "51. At the same time the suppressor electrodes I3 and I4 areconnected in parallel and through the winding 5I which comprises one-half the total secondary of the modulation output transformer 49. In this right hand position of the switch II the anodes 22 and 23are connected through terminals 34and 33 with the outer sides of the windings 38 'and"39. Theinner'sides of these windings are connected through terminals 35 and 36, the midpoint connection being provided through the indicator instrument 45 to the source of constant anode voltage. It willbe seen, therefore, that the primary windings 38 and39 are connected with the anodesZZ and 23 in a balanced push-pull arrangement for transferring vmodulated high :frequency energy with constant .carrier to the load 42.

Now let it be vassumed that it is desired to transmit-Variable carrier, that is, modulation side bands and carrier with side bands. and. Carrier amplitude.

varying in magnitude in accordance with the modulation level and substantially eliminated when the modulation voltage falls to zero. For this condition of operation, the switch 55 is moved into engagement with the Contact terminal 54, whereupon the screen electrodes 9 and I0 are energized in accordance with the instantaneous energy level of the modulation-source 46 operating through the unit 53. The other connections remain the same as for the condition previously described for fixed carrier. Since the screen electrodes 9 and II) now receive their energy from the variable carrier control unit, which in turn is controlled by the varying modulation source, instead of from the constant anode supply'to terminal 51, the output delivered to the load 42 will now be modulation side bands with correspondingly varying or floating carrier The specific circuit arrangement for such form of variable carrier system is also brought out in -my copending application Serial No. 55,978, led December 24, 1935. Y

It may now be Vassumed thatit is desired to effect a third condition of operation for so-called suppressed carrier-transmission. To effect this type of operation, the switch II is moved to the left hand position with the switch contacts I5-29 in engagement with the contact terminals 25-30. In this position of the switch I I, the screen electrodes 9 and I9 are connected in parallel through terminal 2S to the source of constant positive anode voltage supplied to the terminal 57. The suppressor electrode I3 remains in circuit with the winding 5I, while suppressor electrode I4 is connected through switch contact I5 and terminal 25 to the other winding 5U. The windings 5I). and 5I form a balanced-push-pull circuit arrangement for suppressor electrodes of the tubes 4 and 5. In this same position of the switch II, the anodes 22 and 23 are connected in parallel through a balancing potentiometer connected across the Vcontact terminals 27 and 28. The adjustable contactof this potentiometer `is connected to a terminal 29 and to the outer side of winding 38. The inner-side of winding 38 is connected through the switch Contact 25 and terminal 39 to the outer side of winding 39, the inner side of winding Y39 being connected through switch Contact I 9 and thence to contact terminalV 29. In this arrangement, the windings 38 and 39 and the associated anodes 22 'and 23 are connected vin parallel for transferring high frequency energy to the load 42. Since the tubes 4 and 5 now operate in balanced formation, this high frequency energy appears as modulation side bands with the carrier frequency suppressed. The transformation effected by tubes 4 and 5 is also accompanied by the production of even carrier harmonics and related side bands which with a selected modulation side band are eliminated in transmission by lter circuits well known for the purpose and incorporated in the load 32. The detailed circuit arrangement for this form of suppressed carrier transformation is shown in my copending application Serial No. 52,751, filed December 4, 1935.

IIt will nowbe seen that the foregoing discloses a compcsite'transmission system for effecting the transmission of high frequency energy in various senses in accordance with several different operating conditions, any one of which may be utilized as desired. Various modifications and equivalent circuits will readily occur to those skilled in the art but whichwill not depart from the intended scope of my invention. I do not desire to limit myself to the foregoing except as may be pointed out in the appended claims.

I claim:

1. In a radio transmitter employing at least one electron tube having a multiplicity of electrodes, means for supplying sustained oscillations to at least one of said electrodes, a source of modulation energy, means for connecting said source of modulation energy with another of said electrodes, a source of steady current, a rectifier unit controlled by said source of modulation energy, and means for connecting still another of said electrodes with either said source of steady current or said rectifier unit whereby said tube may be rendered operative in at least two diiferent senses for constant carrier or variable carrier transmission of modulated oscillations.

2. A system for producing modulated high frequency energy comprising, a source of high frequency energy, a source of modulation energy, a load circuit, electron tube means, and circuit means having components for interconnecting said sources of energy and said tube means to excite said load with modulated high frequency energy in any of three forms, viz., modulation sidebands with constant carrier, modulation sidebands with variable carrier, or modulation sidebands with carrier suppressed; and means for rendering said circuit means selectively operable in different combinations for eiecting the excitation of said load circuit Vwith such forms of modulated high frequency energy.

3. A system for producing modulated high frequency energy comprising, a source of high frequency energy, a source of modulation energy, a loa-d circuit, electron tube means, circuit means having components for inter-connecting said sources of energy and said tube means and means for rendering said circuit means selectively operable in different combinations for effecting the excitation of said load circuit with modulated high frequency energy in the form of at least one modulation side band and constant carrier, or at least one modulation side band and variable carrier, or at least one modulation side band with carrier suppressed.

4. A radio transmitter comprising, a source of high frequency energy, at least two electron tubes each having cathodes, control electrodes, screen electrodes, suppressor electrodes, and anodes, a circuit energized by said high frequency source and including said control electrodes, a source of constant current, a source of modulation energy, a control unit for producing variable current in accordance with the variations of said modulation energy, switching means for connecting said screen electrodes with said source of constant current or said control unit, an amplier system controlled by said source of modulation energy and including an output circuit having a transformer, switching means for connecting said suppressor electrodes in parallel with said transformer or in push-pull relationship therewith, a load circuit andV transformer therefor, said load transformer having plural primary windings, an energizing connection from said primary windings to said source of constant current, and switching means for connecting said anodes and said windings in parallel or push-pull arrangement,

5. A system in accordance with claim 4 including an arrangement for simultaneously operating said switching means to render said transmitter operative in at least three different conditions for energizing said load circuit with modulated high frequency energy comprising modulation sidebands and constant carrier, modulation sidebands with variable carrier, or modulation sidebands with carrier suppressed.

EDMUND A. LAPORT. 

